Constitutive modelling of skin ageing

The objective of this chapter is to review the main biomechanical and structural aspects associated with both intrinsic and extrinsic skin ageing, and to present potential research avenues to account for these effects in mathematical and computational models of the skin. This will be illustrated through recent work of the authors which provides a basis to those interested in developing mechanistic constitutive models capturing the mechanobiology of skin across the life course

Tension lines of the skin

Skin tension lines are natural lines of tension that occur within the skin as a result of growth and remodeling mechanisms. Researchers have been aware of their existence and their surgical implications for over 150 years. Research in the twentieth century showed clearly, through destructive mechanical testing, that the orientation of skin tension lines greatly affects the mechanical response of skin in situ. More recent work has determined that this anisotropic response is, at least in part, due to the structural arrangement of collagen fibres within the dermis. This observation can be incorporated into mathematical and mechanical models using the popular Gasser-Ogden-Holzapfel constitutive equation. Advances in non-invasive measurement techniques for the skin, such as those based on elastic wave propagation, have enabled patient-specific identification of skin tension lines in an accurate and rapid manner. Using this technique on humans, we show that there is considerable variation in the level of anisotropy as the skin ages. Furthermore, we identify that both the structural arrangement of fibres and the in vivo levels of pre-strain play a significant role in the anisotropic behavior of skin.Peer reviewed2021-05-2

Tension lines of the skin

Skin tension lines are natural lines of tension that occur within the skin as a result of growth and remodeling mechanisms. Researchers have been aware of their existence and their surgical implications for over 150 years. Research in the twentieth century showed clearly, through destructive mechanical testing, that the orientation of skin tension lines greatly affects the mechanical response of skin in situ. More recent work has determined that this anisotropic response is, at least in part, due to the structural arrangement of collagen fibres within the dermis. This observation can be incorporated into mathematical and mechanical models using the popular Gasser-Ogden-Holzapfel constitutive equation. Advances in non-invasive measurement techniques for the skin, such as those based on elastic wave propagation, have enabled patient-specific identification of skin tension lines in an accurate and rapid manner. Using this technique on humans, we show that there is considerable variation in the level of anisotropy as the skin ages. Furthermore, we identify that both the structural arrangement of fibres and the in vivo levels of pre-strain play a significant role in the anisotropic behavior of skin.Peer reviewed2021-05-2

Multiscale characterization of skin mechanics through in situ imaging

International audienceThe complex mechanical properties of skin have been studied intensively over the past decades. They are intrinsically linked to the structure of the skin at several length scales, from the macroscopic layers (epidermis, dermis and hypodermis) down to the microstructural organization at the molecular level. Understanding the link between this microscopic organization and the mechanical properties is of significant interest in the cosmetic and medical fields. Nevertheless, it only recently became possible to directly visualize the skin’s microstructure during mechanical assays, carried out on the whole tissue or on isolated layers. These recent observations have provided novel information on the role of structural components of the skin in its mechanical properties, mainly the collagen fibers in the dermis, while the contribution of others, such as elastin fibers, remains elusive. In this chapter we present current methods used to observe skin’s microstructure during a mechanical assay, along with their strengths and limitations, and we review the unique information they provide on the link between structure and function of the skin